FILE- In this Dec. 30, 2012, file photo, a Seattle Seahawks player high-fives a "12th Man" fan before an NFL football game between the St. Louis Rams in Seattle. On Sunday, Sept. 15, 2013, Seahawks fans will attempt to break the Guinness Book of World Records mark for loudest stadium, or officially "loudest crowd roar at a sports stadium," which was set in 2011 in Turkey at the Ali Sami Yen Sport Complex Turk Telekom Arena during a soccer match between Galatasaray SC and Fenerbahce. The record is 131.76 decibels. (AP Photo/Elaine Thompson, File)

The Packers trotted out safeties M.D. Jennings (11 career starts) and Jerron McMillian, a 2012 fourth-round pick who was making his starting debut. And Kaepernick took advantage: According to Pro Football Focus, Kaepernick completed 9 of 10 passes for 96 yards with two touchdowns when throwing in their direction, posting a 146.3 rating.

He'll get a stiffer test Sunday night in Seattle.

In 2012, the Seahawks allowed the fewest points per game (15.3) in the league and their star-studded secondary was a primary reason. The Seahawks limited quarterbacks to a 71.8 passer rating, the third lowest in the NFL, thanks to a foursome whose members have either earned All-Pro or Pro Bowl honors since 2011: Thomas, fellow safety Kam Chancellor and cornerbacks Richard Sherman and Brandon Browner.

Against Green Bay, Kaepernick had a career-high nine completions of at least 20 yards, with five finding Boldin (13 catches, 208 yards). With Thomas and Chancellor protecting the back end, Seattle doesn't figure to be as susceptible to big plays.

Boldin referenced his former Baltimore teammate, future Hall of Fame safety Ed Reed, when asked how an elite safety - or two - can bolster a defense.

"The communication across the board is a lot better," Boldin said. "They can get guys in the right situation when you have safeties that are real smart. I know, playing with a guy like Ed Reed, we did a lot of film study. He could tell you what a team is going to do just by the way they've lined up."

The Seahawks certainly weren't fooled by the 49ers in December. In a 42-13 loss in Seattle, Kaepernick had the lowest completion percentage (52.8) and passer rating (72.0) of his 11-start career. With two minutes left in the second quarter, the Seahawks led 28-3 and Kaepernick had completed 5 of 14 passes for 41 yards.

On Wednesday, Kaepernick was asked if his struggles in Seattle could be attributed to the strength of the Seahawks' defense.

"We performed bad as a team," Kaepernick said. "We played bad that game. We're going up there to try to prove that's not who we are."

Kaepernick is capable of rewriting the script against Seattle. The Seahawks could be without Browner, who didn't practice Wednesday and sat out Week 1 with a hamstring injury.

On Wednesday, Seattle head coach Pete Carroll noted how Kaepernick has progressed since that Week 16 loss in Seattle. In three postseason games, he posted a 100.9 passer rating and rushed for 264 yards and three touchdowns.

Then he opened 2013 with a flourish: Against Green Bay, he joined Joe Montana as the only 49ers quarterback since 1960 to throw for 400 yards and three touchdowns without an interception.

"You can see the belief in him from the coaching staff," Carroll said. "They really trust him and they really went for it."